Alterations in gene regulation play a key role in the tumorigenic process. Our research centers on two tumor suppressor pathways, p16lnk4a-cycD/cdk4-pRB-E2F and p19Art-mdm2-p53, that control the expression of genes required for cellular proliferation or the tumor surveillance response respectively. We have established a direct link between the pRB/E2F and An7p53 pathways in vivo (Aslanian et al., 2004): specific E2F family members contribute to either the transcriptional repression of Arf in normal cells (via E2F3B) or the transcriptional activation of /A/fin tumor cells (via the activating E2Fs). Experiments in this proposal will use a combination of mouse models (and the resulting cell lines and tumors) and RNAi technology to understand the role of the pRB/E2F pathway in the control of Arf transcription and cellular proliferation. They will also establish how the pRB pathway and cellular transformation influence miRNA regulation and function. There are four goals: (1) To identify the E2F3B represser complex; (2) To understand how the activating E2Fs induce Arf and other "tumor-specific" E2F-responsive genes; (3) To test the requirement for activating E2Fs in the regulation of normal and tumor cells; and (4) To screen for pathways that synergize with pRB in the control of cell proliferation and survival.